La0.7-xDyxSr0.3MnO3(0.00≤x≤0.70)的TCR研究

研究了La位Dy掺杂对La0.7-xDyxSr0.3MnO3(0.00≤x≤0.70)电阻温度系数(TCR)的影响.实验结果表明:Dy掺杂将引起电阻率曲线的急剧变化,导致出现大的TCR;随Dy掺杂的增加,TCR在x=0.30出现峰值,然后随掺杂量的增加逐步降低.体系出现大的TCR,来源于Dy掺杂引起的晶格畸变和额外磁性耦合.     

Investigations of the effect of viscosity of resin on the diffusion of pyrene in silicone polymer coatings using steady state fluorescence technique

The diffusion phenomenon of pyrene in silicone coatings prepared from various commercial silicone resins with different viscosities was investigated using steady state excimer fluorescence technique. The amount of pyrene lost from the coatings by diffusion at different temperatures ranging from 25 to 70 °C was estimated from the excimer emission intensity. The diffusion coefficients (D) and activation energy of diffusion of pyrene in silicone coatings were determined. It was found that the kinetic parameters of pyrene were comparable in all the four silicone coatings and independent of the viscosity of the resin. The D values were lower than those expected for pyrene in PDMS resins in the corresponding viscosity range. This may be attributed to restricted mobility of pyrene due to cross-linking of polymer chains in the cured silicone coatings.     

Gas–liquid partition coefficients and Henry's law constants of methyl mercaptan in aqueous solutions of Fe(II)–CDTA chelate complex

Utilization of ferric chelate complex of trans-1,2-cyclohexanediaminetetraacetic acid (CDTA) for the oxidative scrubbing of H₂S and CH₃SH in Kraft mill streams can be beneficial from the standpoints of iron protection against precipitation and oxygen-mediated regenerative oxidation of the ferrous chelate CDTA. The physical solubility of methyl mercaptan in CDTA–Fe(III) complex cannot be measured directly because of oxidation of the sulfur-bearing gaseous species with the ferric chelate. Therefore, this investigation was carried out to determine the gas–liquid partition coefficients and Henry's law constants of methyl mercaptan in aqueous iron-free CDTA solutions and non-reacting ferrous chelate solutions (CDTA–Fe(II) complex), using the static headspace method with an estimated accuracy of about 2%. Experiments with aqueous solutions of chelate concentrations varying between 38 and 300 mol m⁻³ were carried out at temperatures between 298 and 333 K and atmospheric pressure. It was shown that the methyl mercaptan solubility decreases with increasing temperature for all systems but was not much influenced, in the studied conditions, by the chelate concentration especially at larger temperatures.     

对钠离子有选择性的中性载体

合成了十一种中性离子载体,用它们制成钠离子选择性电极,测定了电极的选择性系数并与文献报道的类似电极进行了比较。     

Aqueous solubilities and octanol-water partition coefficients of binary liquid mixtures of organic compounds at 25°C

From thermodynamics and certain assumptions it is shown that, under the usual experimental conditions, the octanol-water partition coefficient (K_o/w) of a given organic liquid should be the same whether the substance is partitioned neat or as part of a mixture. Measurements of several mixtures of n-propylbenzene (log K_o/w=3.71±0.04)+ethylbenzene (log K_o/w=3.16±0.01) clearly confirm this. It is also shown that the aqueous solubility (S_w) of a neat organic liquid can be related to its aqueous solubility (S _w ), when it is present at volume fraction in an organic liquid mixture, by S _w =S_w, where is its activity coefficient in the organic mixture. The measured S _w values for n-propylbenzene + ethylbenzene (1), n-hexane + nitrobenzene (>1) and di-isopropyl ether + chloroform (<1) are found to be in good agreement with the predicted values (average differences of, respectively, <2%, 8% and 6%). In general, the bounds on S _w are expected to be 0w w.     

Transfer activity coefficient of the proton in water-pyridine mixtures. A comparison of some extrathermodynamic assumptions

Various water-pyridine mixtures have been selected in order to compare several of the most popular extrathermodynamic assumptions involved in the determination of the transfer activity coefficient of the proton, _t(H⁺). Two techniques have been utilized for this purpose: voltammetry [study of the ferrocene, ferricyanide, or thallium(1) systems] and potentiometry at equilibrium (emf measurements of various galvanic cells, including liquid junctions and hydrogen electrode or silver electrode as a test electrode). The assumptions have been classified into various groups [e.g., _t(Z^p+)=_t(Z^q+) or _t(X^–)=_t(Y⁺)], and the values of _t(H⁺) have been experimentally determined in each case. The results vary depending upon the basic assumption (several pH units); less important differences (e.g., 0.5 pH unit) occur within a given group, and this may be assigned to the nature of the reference species chosen. A simple model of solvation has been also examined; the application of the law of mass action to the corresponding equilibrium provides results close to the _t(X^–) =_t(Y⁺)type of assumptions which ultimately leads to most self-consistent results.     

A High-Order Finite Difference Scheme for 3D Unsteady Convection Diffusion Reaction Equations北大核心CSCD

针对三维非稳态对流扩散反应方程,构造了一种高精度紧致有限差分格式,对空间的离散采用四阶紧致差分方法,对时间的离散采用Taylor级数展开和余项修正技术,所提格式在时间上的精度为二阶、在空间上的精度为四阶。利用Fourier稳定性分析法证明了该格式是无条件稳定的。最后给出数值算例验证了理论结果。     

非全局Lipschitz条件下跳适应向后Euler方法的强收敛性分析

本文研究跳适应向后Euler方法求解跳扩散随机微分方程在非全局Lipschitz条件下的强收敛性.通过克服方程非全局Lipschitz系数给收敛性分析带来的主要困难,我们成功地建立了跳适应后向Euler方法的强收敛性结果并得到相应的收敛率.最后,我们通过数值试验对前文所得理论结果做进一步的验证.     

Critical exponents,hyperscaling, and universal amplitude ratios for two- and three-dimensional self-avoiding walks

We make a high-precision Monte Carlo study of two- and three-dimensional self-avoiding walks (SAWs) of length up to 80,000 steps, using the pivot algorithm and the Karp-Luby algorithm. We study the critical exponentsv and 2 ₄ – as well as several universal amplitude ratios; in particular, we make an extremely sensitive test of the hyperscaling relationdv = 2 ₄ –. In two dimensions, we confirm the predicted exponentv=3/4 and the hyperscaling relation; we estimate the universal ratios <R _g ² >/<R _e ² >=0.14026±0.00007, <R _m ² >/<R _e ² >=0.43961±0.00034, and ^*=0.66296±0.00043 (68% confidence limits). In three dimensions, we estimatev=0.5877±0.0006 with a correctionto-scaling exponent ₁=0.56±0.03 (subjective 68% confidence limits). This value forv agrees excellently with the field-theoretic renormalization-group prediction, but there is some discrepancy for ₁. Earlier Monte Carlo estimates ofv, which were 0.592, are now seen to be biased by corrections to scaling. We estimate the universal ratios <R _g ² >/<R _e ² >=0.1599±0.0002 and ^*=0.2471±0.0003; since ^*>0, hyperscaling holds. The approach to ^* is from above, contrary to the prediction of the two-parameter renormalization-group theory. We critically reexamine this theory, and explain where the error lies. In an appendix, we prove rigorously (modulo some standard scaling assumptions) the hyperscaling relationdv = 2 ₄ – for two-dimensional SAWs.     

Determination of the partition coefficients of the nonionic detergent C12E7 between lipid-detergent mixed membranes and water by means of Laurdan fluorescence spectroscopy

The membrane-water partition coefficient of the detergent C₁₂E₇ between water and C₁₂E₇/POPC mixed membranes has been determined by means of steady-state fluorescence spectroscopy. The emission spectra of the fluorescent probe Laurdan were used as an indicator of membrane composition at different membrane concentrations in the sample. The partition coefficient expressed as the ratio of the mole fractions of the detergent in the membrane and water phases is about 6^*10⁵ at low molar ratios of C₁₂E₇/POPC (R _c ) and decreases rapidly with increasingR _c . The limiting detergent content of the lamellar phase (R _c ^* >0.8) is indicated by a minimum ofP(R _c ).